Binding data grid column to dynamic properties

Question

I'm working on a requirement, where any amount of dynamic properties can be added to an entity. These dynamic properties can be shown in a data grid column besides the actual object properties.

To respect the existing architecture, these properties are being stored in a list:

public List<AdaErgaenzungsfeldEntity> Ergaenzungsfelder { get; set; }

In order to bind to each property in the list, I've exposed the values which will be shown in the grid like this:

public Dictionary<Guid, object> ErgaenzungsfeldValues { 
   get { return m_ergaenzungsfeldValues; } 
}

The list and the dictionary are being synchronized when the Ergaenzungsfelder list changes:

private void RefreshErgaenzungsfeldValues() {
   if (m_ergaenzungsfeldValues == null) {
      m_ergaenzungsfeldValues = new Dictionary<Guid, object>();
   }

   m_ergaenzungsfeldValues.Clear();
   foreach (AdaErgaenzungsfeldEntity entity in Ergaenzungsfelder) {
      m_ergaenzungsfeldValues.Add(entity.Ergaenzungsfeld.ID, entity.Value);
   }
}

The binding onto the grid is finally done like this:

List<ErgaenzungsfeldEntity> ergaenzungsfeldEntities = m_presenter.ErgaenzungsfeldService.GetAllErgaenzungsfeldEntities();
   foreach (ErgaenzungsfeldEntity entity in ergaenzungsfeldEntities) {
      m_lstAdas.Columns.Add(new Column {
         Title = entity.Name,
         FieldName = string.Format("ErgaenzungsfeldValues[{0}]", entity.ID)
      });
}

The issue with this implementation is that the dictionary doesn't contain a value for all dynamic fields for all entities, which obviously results in a key not found exception:

System.Windows.Data Error: 16 : Cannot get 'Item[]' value (type 'Object') from 'ErgaenzungsfeldValues' (type 'Dictionary2'). BindingExpression:Path=ErgaenzungsfeldValues[04d1be1c-2d83-48ba-b179-aaa9f0d0f7bc]; DataItem='AdaEntity' (HashCode=-800079524); target element is 'DataCell' (Name=''); target property is 'Content' (type 'Object') TargetInvocationException:'System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary. at System.ThrowHelper.ThrowKeyNotFoundException() at System.Collections.Generic.Dictionary2.get_Item(TKey key) --- End of inner exception stack trace --- at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.Reflection.RuntimePropertyInfo.GetValue(Object obj, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture) at MS.Internal.Data.PropertyPathWorker.GetValue(Object item, Int32 level) at MS.Internal.Data.PropertyPathWorker.RawValue(Int32 k)'

The entity is not aware of all possible fields and thus, it is not possible to add a default value for each dynamic property to every entity.

Question: How can those dynamic values be bound properly to the data grid to avoid the above mention exception?

I've created a small application to illustrate the behavior.

MainWindow.xaml:

<Window x:Class="DynamicdataGridBindingTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:xcdg="http://schemas.xceed.com/wpf/xaml/datagrid"
        DataContext="{Binding RelativeSource={RelativeSource Self}}"
        Title="MainWindow" 
        Height="350" 
        Width="525">
    <Grid>
        <xcdg:DataGridControl 
            Name="m_dataGridControl" 
            AutoCreateColumns="False" 
            AutoRemoveColumnsAndDetailConfigurations="False"
            ReadOnly="True"
            ItemsSource="{Binding TestEntities}">
            <xcdg:DataGridControl.Columns>
                <xcdg:Column Title="Property"
                             FieldName="DefinedProperty" />
            </xcdg:DataGridControl.Columns>
        </xcdg:DataGridControl>
    </Grid>
</Window>

MainWindow.xaml.cs:

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using Xceed.Wpf.DataGrid;

namespace DynamicdataGridBindingTest {
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow {
        private readonly Dictionary<Guid, string> m_dynamicColumnNames = new Dictionary<Guid, string> {
            {Guid.NewGuid(),"DynText"}, 
            {Guid.NewGuid(),"DynBool"}, 
            {Guid.NewGuid(),"DynArray"}
        };

        public ObservableCollection<TestEntity> TestEntities { get; private set; }

        public MainWindow() {
            //Licenser.LicenseKey = "xxx";
            TestEntities = new ObservableCollection<TestEntity>();

            InitializeComponent();
            InitializeEntities();
            InitializedataGridColumns();
        }


        private void InitializeEntities() {
            TestEntity testEntity1 = new TestEntity {
                DefinedProperty = "Property Value 1",
            };
            testEntity1.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(0).Key, "My text");
            testEntity1.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(1).Key, true);
            testEntity1.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(2).Key, new[] { "val1.1", "val1.2", "val1.3" });
            TestEntities.Add(testEntity1);

            TestEntity testEntity2 = new TestEntity {
                DefinedProperty = "Property Value 2"
            };
            testEntity2.DynamicProperties.Add(m_dynamicColumnNames.ElementAt(0).Key, "My text 2");
            TestEntities.Add(testEntity2);
        }

        private void InitializedataGridColumns() {
            foreach (string columnName in m_dynamicColumnNames.Values) {
                m_dataGridControl.Columns.Add(new Column {
                    Title = columnName,
                    FieldName = string.Format("DynamicProperties[{0}]", m_dynamicColumnNames.First(kv => kv.Value == columnName).Key)
                });
            }
        }
    }
}

TestEntity.cs:

namespace DynamicdataGridBindingTest {

    public class TestEntity {
        public string DefinedProperty { get; set; }
        public Dictionary<Guid, object> DynamicProperties { get; private set; }

        public TestEntity() {
            DynamicProperties = new Dictionary<Guid, object>();
        }
    }
}

Which looks like this when being run: enter image description here

Philippe Philippe · Accepted Answer · 2014-07-04T13:13:40

I've solved this issue by implementing a minimal Dictionary implementation, wrapping a Dictionary, but not throwing key not found exceptions:

using System.Collections.Generic;

namespace DynamicdataGridBindingTest {
    /// <summary>
    /// This is a minimal implementation of a Dictionary, which will never throw KeyNotFoundException if trying to access a value for a key which hasn't been set.
    /// </summary>
    /// <typeparam name="TKey">The type of the key.</typeparam>
    /// <typeparam name="TValue">The type of the value.</typeparam>
    public class DictionaryWithReturnValue<TKey, TValue> {
        #region Private Fields

        private readonly Dictionary<TKey, TValue> m_dictionary;

        #endregion

        #region Constructor

        /// <summary>
        /// Initializes a new instance of the <see cref="DictionaryWithReturnValue{TKey, TValue}"/> class.
        /// </summary>
        public DictionaryWithReturnValue() {
            m_dictionary = new Dictionary<TKey, TValue>();
        }

        #endregion

        #region Indexer

        /// <summary>
        /// Gets or sets the value for the specified key.
        /// </summary>
        /// <param name="key">The key.</param>
        /// <returns>The value, if it has been previously set; otherwise default(TValue)</returns>
        public TValue this[TKey key] {
            get {
                TValue value;
                return m_dictionary.TryGetValue(key, out value) ? value : default(TValue);
            }
            set { m_dictionary[key] = value; }
        }

        #endregion

        #region Public Methods

        /// <summary>
        /// Adds the specified key.
        /// </summary>
        /// <param name="key">The key.</param>
        /// <param name="value">The value.</param>
        public void Add(TKey key, TValue value) {
            m_dictionary.Add(key, value);
        }

        /// <summary>
        /// Removes the specified key.
        /// </summary>
        /// <param name="key">The key.</param>
        public void Remove(TKey key) {
            m_dictionary.Remove(key);
        }

        /// <summary>
        /// Clears all the entries.
        /// </summary>
        public void Clear() {
            m_dictionary.Clear();
        }

        #endregion
    }
}

Binding data grid column to dynamic properties

1 Answers